1. Field of the Invention
This invention relates to sensing position of one element relative to another element.
2. Prior Art
Various methods for linear or rotary position sensing are known in various applications. For example, capacitive and inductive position sensors are known.
In one particular application, the movement of a throttle valve in a motor vehicle engine is responsive to the demand of the motor vehicle operator. Preferably, the air/fuel mixture is controlled in response to the throttle position, and numerous sensors for generating a control signal in response to the throttle position have been developed. However, many previously known sensors are contact sensors in which the mechanical movement of the throttle is traced by mechanical displacement of electrical conductors in order to electrically represent the change in throttle positions. Such sensors are subject to mechanical wear that can substantially affect the efficiency and longevity of the electrical conductors and other moving components. Moreover, inherent electrical noise in the output signal limits resolution to a relatively large increment of angular displacement.
An alternative form of sensors are generally referred to as noncontact sensors, but such sensors were not previously well adapted for use in throttle position sensing. For example, previously known capacitive noncontact sensors often rely on changes in the absolute capacitance between two electrodes to generate the control signal responsive to throttle position. However, the absolute value of capacitance can be affected by environmental conditions such as the variations in temperature, moisture, debris, vibration and other factors to which a moving vehicle is subjected. As a result, the accuracy of the sensor decreases as the age and use of the vehicle increases. Moreover, some previously known capacitive resolvers are limited to discrete increment segments of movement within a particular range. Other types of noncontacting sensors such as Hall effect transducers substantially increase the cost or complexity of the sensing apparatus and signal processing for necessary outputs.
It is also known to have a capacitive sensing means with a logic control for driving the sensor in a manner that relies upon relative changes rather than an absolute value of capacitance throughout operation of the sensor. In general, a driver electrode board including a plurality of electrodes is aligned adjacent a rotating member with a coupler for rotational moment with a throttle shaft. An intermediate dielectric having a spatially nonuniform conductive dimension between the driving board and the rotating member provides the relatively changing capacitance between the driver electrode board to an output electrode associated with the rotating member. The association between the electrode and the dielectric only requires that the signal path is confined to pass through the dielectric to the electrode regardless of whether the dielectric and electrode are physically united or separated at a gap. A logic driver coupled to the electrode board develops an input to the sensor body that is output from the output electrode and delivered to a signal processor for generating a phase responsive signal. A logic decoder generates a sensor output representing throttle angular position independent of absolute capacitance between the electrodes.
In particular, the logic driver generates a plurality of driving signals for driving a plurality of electrode segments. In one embodiment, eight segments are driven in incrementally sequenced portions. For example, segments 1-4 may be high while segments 5-8 are low. At the next time interval, the pattern is shifted to charge electrode segments 2, 3, 4 and 5 while 6, 7, 8 and 1 will remain low. The pattern continues, preferably at a high rate, with the rotating logic field set up between the electrode driver board and the rotating output sensing board. The signal-to-noise ratio improves with increasing frequency and its limits depend upon how high of an oscillator speed is conveniently available. The initiating driving signal or input edge is generated when any one pattern, for example, 1, 2, 3, 4 high (repeats). Each sequence of pattern repetition can be called a scan.
The driver provides digital excitation of the sensor. The output of the phase detecting circuit is digital while the angular position is preferably output by an analog signal that conforms with conventional outputs that would be generated by previously known contact sensors conventionally used. A pulse width modulated (PWM) signal, preferably fed through a low pass filter to obtain the analog signal, may be used to provide the analog signal. Alternatively, the pulse width modulated signal may be utilized as compatible with an electronic control module or other apparatus. In addition, digital output may be obtained, for example by a ten bit digital output encoder created by digital logic.